I want to be able to boost 5v from USB all the way up to 25v in small steps and have it s/w controlled by an MCU. What is the best/simplest way to implement this ?

-- Always boost to 25v and then regulate it down with a DAC controlled transistor ? -- Control the boost circuit somehow by outputting different frequency from the MCU? -- Other ways of achieving same goal ?

I would also like to know how to use the ADC to measure current to implement a shut off if a certain current level is exceeded. Would I do that by measure voltage drop over a shunt ?

I am working an an universal device programmer and this is the part I am getting stuck at generating the VPP :?:

"A good scientist is a person with original ideas. A good engineer is a person who makes a design that works with as few original ideas as possible. There are no prima donnas in engineering" - Freeman Dyson